MRP-57 xattr: extended attribute cache implementation

This patch implements an extended attribute cache for
a Lustre client. It is organized as a write-through
cache: reads are performed from cache, updates are sent
synchronously to the MDS. An additional inode bit
is added to protect the cache.

Change-Id: I6f819dad617d92e5ae6ce6982061778eb9b021e3
Reviewed-on: http://morpheus.xyus.xyratex.com:8443/gerrit/213
Reviewed-by: Artem Blagodarenko <Artem_Blagodarenko@xyratex.com>
Tested-by: Jenkins
Reviewed-by: Alexey Lyashkov <Alexey_Lyashkov@xyratex.com>
Tested-by: Elena Gryaznova <Elena_Gryaznova@xyratex.com>
Reviewed-by: Vitaly Fertman <Vitaly_Fertman@xyratex.com>
MRP-997 MDS can't umount with blocked flock

Add ldlm_flock_blocking_unlink() to
ldlm_resource_unlink_lock().
It is needed to be called during server side
cleanup_resource()

Change-Id: I30de6473c44e1249d461014abd01c44b117ee937
Signed-off-by: Andriy Skulysh <Andriy_Skulysh@xyratex.com>
Reviewed-on: http://morpheus.xyus.xyratex.com:8443/gerrit/411
Tested-by: Jenkins
Reviewed-by: Alexander Boyko <Alexander_Boyko@xyratex.com>
Tested-by: Alexander Lezhoev <Alexander_Lezhoev@xyratex.com>
Reviewed-by: Vitaly Fertman <Vitaly_Fertman@xyratex.com>